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Asymmetric Reduction Of Carbonyl Compounds To Chiral Alcohols With Biocatalysis

Posted on:2010-04-19Degree:MasterType:Thesis
Country:ChinaCandidate:L M SunFull Text:PDF
GTID:2181360278458113Subject:Biochemical Engineering
Abstract/Summary:PDF Full Text Request
Chiral alcohols are important building blocks for the synthesis of chiral pharmaceuticals. Asymmetric reduction of carbonyl compounds to chiral alcohols with biocatalysis has the advantages of mild reaction condition and high stereoselectivity.Response surface methodology was applied to optimize medium constituents for the asymmetric whole cell biotransformation by Candida tropicalis 104. This obtained strain was screened out from four yeasts and two yeast-like filamentous fungi for microbial reduction of 1-[3,5-bis(trifluoromethyl)phenyl]ethanone to(S)-1-[3,5-bis(trifluoromethyl)phenyl]alcohol, with the enantiomeric excess(e.e.) reached more than 99.9%. Based on single factor experiments, Fractional factorial design was used to evaluate the effects of medium components on enzyme activity of Candida tropicalis 104. The results show that yeast extract, glucose and NH4Cl were the most powerful factors among the six tested variables that influence intracellular enzyme activity for the biotransformation process. Based on the experimental results, the path of steepest ascent was undertaken to approach the optimal region of these factors. Central composite design and response surface analysis were subsequently employed for further optimization. The optimal medium for Candida tropicalis 104 was composed of (in g/L): glucose 47.14, yeast extract 13.25, NH4Cl 2.71, MgSO4·7H2O 0.4, KH2PO4 1, K2HPO4 1. Under the optimum conditions, the maximum enzyme activity of 852.75 U/L in theory and 851.13 U/L in the experiment were obtained, with an increase of 65.2% compared to the original medium components.Secondly, substrate concentration, the different co-substrate and co-substrate concentration, cell concentration and reaction time were investigated to improve the processing of asymmetric reduction, thus the optimum technique of production was obtained.Thirdly, based on the research of configuration reverse, (R)-1-[3,5-bis(trifluoromethyl)phenyl]alcohol was successfully obtained from (S)-1-[3,5-bis(trifluoromethyl)phenyl]alcohol by chemical-catalytic.Finally, the space-time productivity is very low due to the toxicity of the substrate and product to the cell, which prohibits the reaction from proceeding at a high substrate concentration. Through introducing macropore adsorbing resin, the control substrate and product density avoids the high density substrate and product to cell’s toxicity, then enhancement reaction space-time productivity. The experiments showed that the substrate and product did have obvious toxicity to yeast cell, inhibited reaction activeness, when asymmetric reduction of 1-[3,5-bis(trifluoromethyl)phenyl]ethanone to(S)-1-[3,5-bis(trifluoromethyl)phenyl]alcohol by Candida tropicalis 104 was chosen as the model reaction. The introduction resin may remarkably promote reaction advance. The initial1-[3,5-bis(trifluoromethyl)phenyl]ethanone concentration could be increased to 150 mmol/L when the appropriate amount of AMBERLITE XAD7HP resin was used. The high concentration of EOB and EHB prohibits the reaction from proceeding, This reaction could be improved with introducing AMBERLITE XAD1600 resin.
Keywords/Search Tags:Candida tropicalis 104, asymmetric reaction, (S)-1-[3,5-bis(trifluoromethyl)phenyl]alcohol, (R)-1-[3,5-bis(trifluoromethyl)phenyl]alcohol, (R)-ethyl-3-hydroxybutyrate
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